1. Field of the Invention
The subject matter of the invention includes a method and an apparatus for cleaning an inner wall of a mold. In particular, the present invention includes a method and apparatus for cleaning an inner wall of a mold for producing vehicle tires, by means of dry-ice pellets.
2. Related Art
An extremely wide range of cleaning methods are known for the purpose of cleaning metallic components. The cleaning methods may be subdivided into physical and/or chemical cleaning methods. The chemical cleaning methods are based on the particles of dirt which adhere to the component being subjected to a chemical reaction by the action of a cleaning agent and being detached from the component as a result. Special apparatuses, which are complex and very expensive, are necessary for carrying out chemical cleaning. As a result of the generally aggressive cleaning media, only high-quality, chemically resistant materials can be used in such cleaning apparatuses. Cleaning apparatuses which operate on a chemical basis are also subject to stringent legal regulations which can only be met by considerable outlay on equipment.
As an alternative to chemical cleaning, components may be cleaned by physical methods. In this case, the contaminants are removed mechanically from the component by abrasion. Abrasive media may be used for removing contaminants from a component. Abrasive media may be in the form of sand, cork or glass. Probably best-known method of mechanically removing contaminants from a component is the so-called sand-blasting method. Sand blasting is preferably carried out in separate chambers, in which the component is introduced and blasted by a sand-blasting device.
DE 43 14 264 C1 discloses a sand-blasting device which is suitable for cleaning rims of motor-vehicle wheels. The motor-vehicle rim which is to be cleaned is arranged in a housing, the base of which is of funnel-like design. The funnel-like base of the housing is connected to a sand-collecting area by a connecting duct. The sand-collecting area is connected to the sand-blasting device via a sand-feed line. The sand-blasting device may be located in the housing. According to DE 43 14 264 C1, it is possible for only the front, nozzle-like end of the sand-blasting device to project into the housing. This configuration of the apparatus for cleaning rim of motor-vehicle wheels minimizes the sand consumption since the cleaning sand runs around in a closed circuit.
In addition, U.S. Pat. No. 4,603,515 discloses a means for removing a layer of corrosion from the walls of the booster of a bomb. The layer of corrosion is removed by sand blasting. In order to remove the sand from the shell of the bomb, a vacuum means is provided.
Sand-blasted components subsequently have to be subjected to careful cleaning in order to ensure that the fine sand is removed from all possible niches of the component. The use of sand blasting for cleaning molds, in particular molds for producing plastic parts, is very costly because of the relatively high cost outlay for cleaning, which is necessary in order to remove the sand from all possible niches of the mold. The possible ways of cleaning components which have been described above require that the component which is to be cleaned is provided separately. In the case of molds of plastic-processing machines or molds for producing vehicle tires, then it is necessary for the mold to be removed from the machine. Once the cleaning operation has been carried out, the machine has to be set up anew. This procedure for cleaning molds is costly and results in the operating time of the machine being reduced considerably.
In order to avoid the removal and reinstallation of a mold, it is also known for such molds to be cleaned manually. This method of cleaning is hazardous to the personnel carrying out the cleaning since aerosols are produced during the cleaning operation, which may have an adverse effect on health if suitable protective measures are not provided for the personnel. In addition, cleaning of the inner wall of the mold can be difficult due to a multiplicity of narrow and short depressions.
It is also known for components to be cleaned by means of dry-ice pellets. Dry ice is carbon dioxide which has been converted into the solid physical state. Under atmospheric pressure, dry ice changes directly from the solid physical state into the gaseous state without any melt liquid being produced. Cleaning with dry ice thus has the advantage that no residues of the dry ice remain in the mold. With the aid of a carrier medium, e.g. air or nitrogen, the dry-ice pellets are blasted, via a cleaning nozzle, against the component which is to be cleaned. The pellets remove the contaminants from the wall of a component. The mechanical removal of the contaminants is assisted by the refrigerating action of the dry ice, which is at a temperature of at least -78.5.degree. C. During cleaning there is a high emission of sound. The source of the sound emission is the cleaning nozzle, through which the cleaning jet which contains dry-ice pellets emerges. A reduction in the sound emission at the cleaning nozzle has been achieved by a further development of the cleaning nozzle. However, the sound emission is still of such a magnitude that cleaning of a component can only be carried out if costly sound-insulation measures are taken.